Joao S Amaral

Joao S Amaral
University of Aveiro | UA · CICECO - Aveiro Institute of Materials

PhD.

About

115
Publications
18,196
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1,555
Citations
Additional affiliations
January 2002 - present
University of Aveiro
January 2002 - present
Universidade do Porto
Education
September 2005 - December 2009
University of Aveiro
Field of study
  • Physics

Publications

Publications (115)
Data
Full-text available
We investigate the magnetocaloric effect dependency on the most important microscopic parameters of ferromagnetic materials, such as the Curie temperature (T-C), the spin value (J), and the magnetic field change (Delta H). Second- and first-order phase transition systems are considered, using the Bean-Rodbell model [A. Arrott, Phys. Rev. 108, 1394...
Article
Full-text available
In striving for mass production of magnetocaloric materials for refrigeration applications, one has to face the fact that these will not be laboratory-grade materials, and will necessarily present (at the very least) composition gradients due to lower quality precursors. One can expect some probable consequences from this, namely that the maximum v...
Preprint
Full-text available
A Monte Carlo method to estimate the Joint Density of States g(E,M) of the Ising and Ising-like models is presented. The method is applied to the well-known 2D Ising model, and is shown to be accurate, efficient, and embarrassingly parallel. The method presented offers major improvements over existing approaches. Furthermore, we obtain g(E,M) estim...
Article
The competition between the stability of the cubic and hexagonal full Heusler alloys and the implications concerning their magnetic properties were systematically studied through the detailed structural and magnetic characterization of the Fe2Mn(Si1−xGex) system. This system was specifically chosen as the parent compositions are cubic (x = 0) and h...
Article
The search for magnetoelectric materials typically revolves around the struggle to make magnetic and ferroelectric orders simultaneously coexist in the same material, using either an intrinsic or an extrinsic/composite approach. Via ab initio calculations of a prototypical Fe/BaTiO3 interface, we predict that it is possible to tune the magnitude of...
Article
Polycrystalline lead-free (1-x)BaFe12O19–x(K0.5Na0.5)NbO3 magnetoelectric ceramic composites (x = 10, 20 and 30 wt%) were fabricated for the first time, comparing various synthesis techniques, namely solid state reaction, sol-gel, co-precipitation and citrate combustion methods for the synthesis of the ferrite phase. As well as the four synthesis r...
Conference Paper
Full-text available
O número de cirurgias primárias e de revisão da Artroplastia Total da Anca (ATA) e Artroplastia Total do Joelho (ATJ) tende a aumentar. Estes dados têm motivado o desenvolvimento de implantes instrumentados com capacidade de monitorizar o estado da interface osso-implante e de aplicar estímulos biofísicos personalizados quando são detetados estados...
Article
In this study, magnetic nanosorbents consisting of magnetite (Fe3O4) cores coated with trimethyl chitosan (TMC)-silica hybrid shells were synthesized using a one-step coating procedure, and their application in the adsorptive removal of glyphosate (GLY) from artificial (ultra-pure) and real water (wastewater) samples was investigated. In synthetic...
Article
Full-text available
A calcium phosphate (CaP)-based scaffold used as synthetic bone grafts, which smartly combines precise dimensions, controlled porosity and therapeutic functions, presents benefits beyond those offered by conventional practices, although its fabrication is still a challenge. The sintering step normally required to improve the strength of the ceramic...
Article
The potential thermal regulation effect of rigid polyurethane (RPU) foams can be enhanced by the incorporation of phase change materials (PCM). The main goal of the present work is to evaluate the thermal characteristics of RPU panels using two different types of PCM (a commercial one and another based on paraffin and calcium carbonate) and to quan...
Article
Many modern technologies require permanent magnets with combinations of properties that cannot be met by conventional metallic or ceramic magnets. Ferrite/polymer composite magnets are a type of rare-earth free magnet with a wide range of magnetic and material property combinations. The uncertainty surrounding the supply and pricing of rare-earth e...
Article
The search for better and inexpensive magnetoelectric materials is now commonplace in solid state physics. An intense coupling between technologically viable electric and magnetic properties, embedded in a single material, is still an attribute greatly pursued by the scientific community. Following this line of thought, using DFT, the study of a sp...
Preprint
Full-text available
The sensitivity and automation capabilities of modern superconducting quantum interference device (SQUID) magnetometers are currently unmatched. The measured moment values are, however, prone to deviations from their actual value due to geometric effects, namely sample size, shape, and radial offset. This is well known, and a knowledgeable operator...
Article
The use of poly(vinyl chloride) (PVC) structural layers incorporating phase change materials (PCM) for latent heat thermal energy storage (LHTES) has become more attractive in the recent years compared to other supporting materials. In this study, PVC layers with different types of PCM were prepared using blending and compression moulding methods....
Article
Full-text available
Prototyping innovative energy devices is a complex multivariable dimensioning problem. For the case of magnetocaloric systems, one aims to obtain an optimized balance between energy conversion performance, useful power generated, and power consumed. In these devices, modeling is entering a mature phase, but dimensioning is still time consuming. We...
Preprint
Full-text available
Mn-Zn ferrite nanoparticles have been subject of increasing research due to their desired properties for a wide range of applications. These properties include nanometer particle size control, tunable magnetic properties and low toxicity, providing these ferrites with the necessary requirements for cancer treatment via magnetic hyperthermia. Powder...
Article
DOWNLOAD FREE FOR 50 DAYS AT https://authors.elsevier.com/c/1aWWQ~2-EzKM- . Hexagonal ferrites can be employed in a multitude of applications, the most common hexaferrites are the M ferrites such as BaFe12O19 (barium hexaferrite, BaM). It is known that if Fe3+ is substituted with a combination of Ti4+/Co2+ the coercivity of BaM can be reduced to pr...
Article
Heusler compounds are one of the most versatile families of materials, showing a wide range of technological applications. Here we present a pure in‐silico approach to fully study the physical properties of this promising family of materials as potential competitive magnetocalorics. The temperature and field dependence of the magnetization of three...
Article
The major aim of the present study is to improve the thermal characteristics of polyurethane foams (PUFs) that have been almost exclusively used for thermal insulation purposes but can also play a role in potential thermal energy storage components as a matrix material. To overcome the low thermal conductivity of the of PUFs matrix, a synthesized p...
Article
Half-metallic compounds present two spin bands with contrasting behaviors, resulting in 100% of spin polarization at the Fermi level; property of crucial importance for applications in spintronic devices. Materials presenting this characteristic are, for instance, some Heusler compounds, mainly Co2-based compounds, which have interesting properties...
Article
Water contamination with antibiotics is a serious environmental threat. Ciprofloxacin (CIP) is one of the most frequently detected antibiotics in water. Herein, silica-based magnetic nanosorbents prepared using three seaweed polysaccharides, alginic acid, κ- and λ-carrageenan, were developed and evaluated in the uptake of ciprofloxacin. The sorbent...
Article
Recent studies highlight the ability of inductive architectures to deliver therapeutic magnetic stimuli to target tissues and to be embedded into small-scale intracorporeal medical devices. However, to date, current micro-scale biomagnetic devices require very high electric current excitations (usually exceeding 1 A) to ensure the delivery of effic...
Article
Recent economic and environmental concerns have prompted intensive research on the development and optimisation of rare-earth free permanent magnets, in particular of ferrites. M-type barium hexaferrites (BaFe12O19, BaM) are a type of technologically important, low-cost permanent magnet, with high Tc and high resistance to oxidation and corrosion....
Conference Paper
Full-text available
This work provides, for the first time, a new small-scale magnetic stimulation system that requires lower excitation of electrical current.
Article
Magnetic particles were successfully synthesised by a new and simple one-step auto-ignition method, with octylamine as organic fuel and iron nitrate nonahydrate as an oxidant, both in an aqueous solution. After synthesis and stabilising at 550 °C in reduced atmosphere, the samples consisted of mostly well crystalline magnetite (Fe3O4), with a small...
Article
Due to the dynamic nature of the active magnetic regenerative mechanism in magnetocaloric refrigeration, the thermal conductivity of the refrigerant is a critical parameter. Experimental studies have shown how the thermal conductivity of high-performance magnetic refrigerants can drastically change around their Curie temperatures (TC). However, thi...
Article
Among all ferroic-based thermotechnologies, magnetocaloric refrigeration has become one of the most reported alternatives to vapor-compression systems. Hence, the modeling, and respective computation, of magnetocaloric systems has become of paramount importance in designing new devices. The need to optimize various adjustable model parameters makes...
Article
Research on topological defects in hexagonal manganites exposed uncovered properties of topologically protected domains and domain walls. Topological defects of h-REMnO3 oxides (RE=Lu-Dy and Sc, In) modify essential multiferroic properties. Despite wide research with single crystals of stoichiometric composition, for the case of polycrystalline cer...
Article
So far, all ferroic-based refrigerator prototypes have relied either in fluids or thermally switchable components as main heat exchangers, which brings some issues in terms of their applicability, such as the use of pumps for moving the fluid and the availability of thermally switchable components. We show that such heat exchangers are not necessar...
Article
Materials with strong magneto-volume coupling can present a coupled first-order magnetic and structural transition and a giant magnetocaloric effect. The trade-off of the resulting increased entropy change is hysteresis, and incomplete transition when the applied field is <2 T, implying that the full cooling capacity of the refrigerant is not harne...
Article
FREE DOWNLOAD FOR 50 DAYS AT: https://authors.elsevier.com/a/1Xtx83IWkbujyv Nanoparticles of zinc-cobalt spinel ferrite Co0.5Zn0.5Fe2O4 (CZFO) were prepared by co-precipitation route, and the effect of the addition of various surfactants (ethanol, PEG, CTAB and acetic acid; surfactant:metals = 0.5:1) on their magnetic and optical properties were in...
Article
Full-text available
A combination of sol–gel synthesis and thermal decomposition was developed for preparing nanosized, perovskite‐type LnFeO3 (Ln = Eu, Gd, Tb) powders. Perovskite‐type powders with crystalline particles of 100 nm average size, as determined by transmission electron microscopy (TEM), could be obtained after a thermal treatment at 800 °C. The perovskit...
Chapter
Magnetoelectric composite ceramics were prepared to study their phase compatibility, magnetic and piezoelectric/ferroelectric properties, and coupling between magnetic and ferroelectric properties. The synthesis of various BaFe12O19 (BaM) and SrFe12O19 (SrM) hexaferrites was undertaken with different sintering temperatures, and exploring four diffe...
Article
Full Heusler alloys are well known to either crystallize in a cubic structure (Cu2MnAl-type), or present tetragonal distortions. Both structure types present interesting properties, like room temperature magnetic memory shape effect and/or remarkable magnetocaloric effect, mainly ruled by strong magnetostructural coupling. Due to this interplay, ou...
Article
Structural, dielectric and magnetic properties of dense Dy-substituted strontium titanate ceramics are investigated. In the Sr1-1.5xDy x TiO3 system, incorporation of Dy onto the Sr site is confirmed by a linear decrease of the lattice parameter up to x =0.05. Dielectric spectroscopy analysis of Sr1-1.5xDy x TiO3 ceramics reveals four relaxations....
Article
Full-text available
Although the number of computational investigations of heat transfer processes involving non-conventio-nal effects has been increasing for the past years, mainly due to the modeling of caloric systems such as magnetocaloric devices, an open source package dedicated to such dynamics is still unavailable. So far, all reported simulations of caloric s...
Article
In this report, a successful thermodynamical model was employed to understand the structural transition in Er5Si4, able to explain the decoupling of the magnetic and structural transition. This was achieved by the DFT calculations which were used to determine the energy differences at 0 K, using a LSDA+U approximation. It was found that the M struc...
Article
Structural, dielectric and magnetic properties of dense Gd-doped strontium titanate ceramics prepared by the conventional mixed oxide method are studied. Lattice parameter is found to decrease linearly in the Sr1-1.5xGd xTiO3 system, confirming the incorporation of Gd onto the Sr site of the perovskite lattice of strontium titanate up to x = 0.05....
Article
Alnico V thin film samples with the thickness of 100 nm were prepared by radio-frequency sputtering on Si substrates with and without a SiO2 layer. Heat treatment of the as-deposited thin films in above ambient pressure in an Ar atmosphere at a temperature range of 600–900°C, followed by quenching and/or slow cooling, leads to higher coercivity val...
Article
In this report the magnetic, atomic structures and spin-lattice coupling have been thoroughly studied through high magnetic field magnetometry, Synchrotron X-ray diffraction under applied magnetic field and magnetostriction measurements in the Tb5Ge4 compounds. A field induced phase transition from an antiferromagnetic towards a ferromagnetic order...
Article
A study on the underlying interaction mechanisms between lattice constants, magnetic and dielectric properties with inhomogeneities or internal interfaces in hexagonal, offstoichiometric LuMnO3 oxide is presented. By increasing Mn content the a-axis constant and volume of the unit cell, the antiferromagnetic (AFM) Néel temperature, TN, and frustrat...
Article
The magnetic properties tuning and volume dependence in the series of quaternary full Heusler alloys with formula Co2Cr1-xYGa (Y = Ti, V, Mn, Fe, Co, Ni) were studied with a detailed first-principles exploration. We employ the density functional KKR method with the coherent potential approximation, estimating effective Heisenberg exchange constants...
Article
Determining and acting on thermo-physical properties at the nanoscale is essential for understanding/managing heat distribution in micro/nanostructured materials and miniaturized devices. Adequate thermal nano-characterization techniques are required to address thermal issues compromising device performance. Scanning thermal microscopy (SThM) is a...
Article
We present for the first time a nonaqueous sol–gel route to produce ultrasmall (<2 nm) magnetic bimetallic CoPt3 nanoparticles (NPs). The one-pot procedure is carried out at low temperature (180 °C) using benzyl alcohol, acting as both reducing agent and solvent. The highly monodisperse CoPt3 NPs were investigated with innovative advanced X-ray met...
Article
Since the discovery of giant magnetocaloric materials, it has become clear that magnetovolume coupling can lead to a large increase to a material's magnetocaloric effect, and so, to high-performance magnetic refrigerants. A simple and computationally inexpensive approach to gauge magnetovolume effects is via the Bean-Rodbell model, where a Curie te...
Conference Paper
The power and efficiency of magnetic refrigerators and thermomagnetic motors depend on their operating frequencies. To improve the efficiency of these machines, it is necessary to design the regenerators/heat exchangers so to present heat transfer as high as possible, allowing higher operational frequencies. In several machines, a fluid flowing thr...
Article
Manganites with the formula La1-xCaxMnO3 for 0.2 < x < 0.5 undergo a magnetic field driven transition from a paramagnetic to ferromagnetic state, which is accompanied by changes in the lattice and electronic structure. An isotropic expansion of the La0.75Ca0.25MnO3 cell at the phase transition has been observed experimentally. It is expected that t...
Article
We present a simple analysis based on the molecular field theory and on the Bean-Rodbell model to justify the magnetocaloric effect (MCE) on La0.7Sr0.3Mn0.9Ti0.1O3. The modeling the magnetic properties of the La0.7Sr0.3Mn0.9Ti0.1O3 was investigated. Using the Brillouin function we have determined the mean field exchange parameter λ and the total an...
Article
Barium M-type hexagonal ferrite (BaM, BaFe12O19) is an immensely important magnetic material, which we have successfully made from the simple valorisation of Fe-rich industrial waste from steel wire drawing, with addition of BaCO3 and heating in air to 1000 ºC. The optimum ratio of Fe.Ba (producing 86 wt% BaM) was found to be 11:1 (non-stoichiometr...
Article
Inorganic pigments are substances that develop colour in organic solids such as ceramics and glazes, and are usually a complex mixture of oxides, and relatively low cost. Their chromatic properties have been extensively studied, yet surprisingly the magnetic and electrical properties of these economic and common materials have been neglected, despi...
Article
Nanocrystalline powders (around 100 nm) of La0.67Ba0.33CrxMn1-xO3 (x≤0.17) perovskites have been synthesized by the sol-gel based Pechini method at low temperature. Structure, resistivity, magnetization, and magneto-transport properties were systematically investigated as a function of Cr doping. Rietveld refinement of fitted and observed X-ray dif...
Article
Assessing Segregation Effects on Multiferroic Properties of Antiferromagnetic-Weak Ferromagnetic Coupled Systems by Analytical HRTEM - Volume 22 Issue S4 - J. M. Vieira, A. Baghizadeh, J. S. Amaral, J. N. Gonçalves, B. A. Almeida, M-G. Willinger, V. S. Amaral
Article
Scanning Thermal Microscopy: Nano-localized Thermal Analysis and Mapping of Surface and Subsurface Thermal Properties - Volume 22 Issue S4 - M. J. Pereira, J. S. Amaral, N. J. O. Silva, V. S. Amaral
Article
Full-text available
Bi2-xPbxBa2Co2Oy (x=0.0, 0.2, 0.4, and 0.6) misfit compounds were grown by the laser floating zone technique. Microstructural analysis has shown the formation of thermoelectric grains together with high amount of secondary phases. Thermoelectric grains orientation is increased until 0.4Pb, while further substitution drastically destroys the prefere...
Article
Full-text available
A flexible, adaptable, economical and easily scalable processing route, allowing microstructural control, is presented. It involves classical solid state sintering method and addition of liquid promoting compound. Controlled porosity and high thermoelectric performance have been attained in Ca3Co4O9 by K2CO3 additions, drastically improving the sin...
Article
Full-text available
We report polycrystalline BaTiO3 with cooperative magnetization behavior associated with the scarce presence of about 113 atomic ppm of Fe ions, clearly displaying magnetoelectric coupling with significant changes in magnetization (up toδM/M ≈32%) at the ferroelectric transitions. We find that Fe ions are segregated mostly at the interfaces between...
Article
Full-text available
We explore the thermodynamics of the 2-D Ising model from a random path sampling method. We show how convergence of free energy and magnetization is obtained in a number of sweeps orders of magnitude below the number of total configurations. The effects of external parameters, such as magnetic field (H) and temperature (T) are accounted in a comput...
Article
Full-text available
In the present work, spontaneous magnetization is observed in the inverse magnetic susceptibility of La0.7Ca0.3MnO3 and La0.7Ba0.3MnO3 compounds above TC up to a temperature T*. From information gathered from neutron diffraction, dilatometry, and high-field magnetization data, we suggest that T* is related to the transition temperature of the low-t...
Article
Full-text available
In the present work, spontaneous magnetization is observed in the inverse magnetic susceptibility of La$_{0.7}$Ca$_{0.3}$MnO$_3$ and La$_{0.7}$Ba$_{0.3}$MnO$_3$ compounds above $T_C$ up to a temperature $T^*$. From information gathered from neutron diffraction, dilatometry, and high-field magnetization data, we suggest that $T^*$ is related to the...